There are several advantages of using light emitting diodes for street lighting. However, such luminaires are supported elevated from streets at a sufficient height whereby the LED's are required to generate sufficient power to provide the necessary lumens on the plane to be lit, herein street lanes and adjacent spaces. The lumen generated by the LED's need to meet established standards to provide a uniform photometric distribution pattern and this according to the type of road to be lit whereby to accommodate the visual needs of drivers and pedestrians. It is also important to minimize glare and light pollution. An advantage of using LEDs is that the electric energy consumed is much reduced as compared to conventional sources, such as sodium, metal halide and mercury light high pressure. Also, LED luminaires require very little maintenance if the critical thermal temperature of the LED's is maintained within manufactured specification whereby the LED's can achieve their life-time rating which is considerably more than conventional luminaires. Therefore, all of this translates in considerable savings in power and cost to maintain LED luminaires.
When using LED's for street luminaires it is important that the street lamps or luminaires meet the photometric requirements of specific applications in a most energy efficient manner and there are regulations concerning the performance of such street lighting application when using LED light sources. The metric Luminaire System Application Efficacy (LSAE) was devised to evaluate the delivery of light where needed in a most energy-efficient manner. LSAE is a good predictor of energy efficiency to rank individual luminaires or groups of luminaires staggered in a specific lay-out in relation to a roadway. The American National Standard practice for roadway lighting. RP-08-00 (IESNA 2000) has published a Table of recommended maintain-average horizontal illuminance levels for different types of roads, pavement and pedestrian conditions. These recommendations are published in a document entitled “Recommendations For Evaluating Street and Roadway Luminaires”, volume 10. Issue 1, April 2011. Therefore, when constructing street luminaires using light emitting diodes as the light source, it is of utmost importance that these recommendations be met. It is also important to note that the more luminous flux falling on a plane to be lit, otherwise known as the task plane, the better maximum pole spacing can be achieved thereby further reducing cost of a street luminaire system for a specific pavement classification as defined by the IESNA recommendations.
It is also important with street lighting to reduce glare which is a critical issue in street and roadway luminaire design for illuminating large areas at night. It is therefore important to consider the luminous flux exiting a luminaire at a certain angle, the height of the luminaire from the task plane to be lit and the spacing between luminaires whereby to evaluate glare. This is important also in the calculation of pole spacing for given sets of conditions as set forth in the above-mentioned recommendations published by IESNA. Light that extends to angles greater than 90° from the luminaire is considered waste light or light pollution and the luminaire needs to be designed to substantially reduce or eliminate this light pollution and thereby resulting in an increase in lumens generated in a desired oriented photometric distribution pattern. The above referred-to Publication further includes Tables wherein pole mounting and spacing requirements have been established in relation to input power, and luminous efficacity (lumens/watt). Such Table establishes in the number of poles per mile and the power demand in kilowatts per mile.